Hydrogen Annealing Effects on the Optical Absorption Loss and Lattice Constant of Ca-Doped YIG and BiGdAlGaIG Films

The effects of annealing in an H
₂
atmosphere on the optical absorption losses and lattice constants of Ca- and Si-doped YIG and Ca-doped (BiGd)
₃
(FeAlGa)
₅
O
₁₂
films grown by LPE, were studied. Hydrogen annealing was carried out at 150 to 500°C for 22 hours. The absorption losses and lattice constants in YIG films with poor impurities or with Si doping did not change with H
₂
annealing at 150 to 450°C; however, the values in Ca-doped YIG and Bi-substituted garnet films changed notably. The changes in absorption loss are explained by the reduction of Fe ions. The minimum value of the absorption loss was about 250 dB/cm at λ = 0.8 μm for both Ca-doped and Ca-free garnet films. These results show that H
₂
annealing is effective for obtaining iron garnet films with a high figure of merit. The lattice constant increased with increasing annealing temperature, and only in Ca-doped YIG films did it decrease drastically, at 450°C.